Frail older patients are at risk for adverse consequences from medications or other external stresses. No single marker, such as age or physical disability, or laboratory test can identify this group of patients. As a result, screening questionnaires have been developed and successfully used by nurses to help identify frail older patients upon admission to a hospital. A very short, 7-item screen with questions concerning cognitive ability, physical mobility, nutrition, number of medications used and hospitalisation within the previous month, was able to identify those patients who were more likely to be discharged to a nursing home, die, or incur a large hospitalisation cost for the institution. While the number of medications used was not an independent predictor of the outcome measures studied (e.g. discharge to a nursing home), data from the literature show that the number of medications prescribed is related to iatrogenic complications in older patients, and specific impairments in mobility and cognition. The proper choice and prescribed dose of a medication is extremely important in frail older patients who, for instance, are at increased risk from hip fracture with some benzodiazepines, and who have markedly diminished clearance of some drugs. A systematic approach is suggested for the prescription of medications in frail older persons which will help achieve optimal pharmacotherapy by using a limited number of medications, thoughtfully selecting medications which will not impair function, and prescribing an appropriate dose based on pharmacodynamic and pharmacokinetic changes that occur with age.